1. Field of the Invention
The present invention relates generally to power supplies and, more specifically, the present invention relates to trimming a power supply for increased accuracy in the maximum deliverable power of the power supply.
2. Background Information
Most battery operated portable electronic products such as cell phones, personal digital assistants (PDAs), etc., require a low power alternating current (AC) to direct current (DC) charger power supply with a constant voltage and constant current (CC/CV) characteristics for charging batteries. In known power supplies, the peak current limit threshold and operating frequency are trimmed independently during manufacturing. The two parameters have their own specifications without any relationship to each other. Other known power supplies employ discrete solutions where the tolerances of components like resistors, and capacitors will affect the peak current limit threshold, and the operating frequency, and by doing so also affecting the maximum delivered power.
Methods and apparatuses for trimming a power supply are disclosed. In one aspect of the invention, a power supply regulator has a peak current limit detection threshold and an operating frequency. In the one embodiment, either the peak current limit threshold or the operating frequency are adjusted specifically to maintain the product of the square of the peak current limit and the operating frequency substantially constant from one power supply controller to another. In one embodiment, the power supply regulator is used to implement a flyback converter. In another embodiment, the power supply regulator is used to implement a buck converter. In one embodiment, the power supply regulator operates with a substantially constant frequency under all operating conditions. In another embodiment, the power supply regulator operates with a substantially constant frequency under a fixed range of operating conditions.
In another aspect of the present invention, a power supply regulator has a peak current limit detection threshold and an operating frequency. The peak current limit threshold and/or the operating frequency are adjusted during the manufacture of the power supply controller to maintain the product of the square of the peak current limit and the operating frequency substantially constant from one power supply regulator to another. In one embodiment, the power supply regulator is used to implement a flyback converter. In another embodiment, the power supply regulator is used to implement a buck converter. In one embodiment, the power supply regulator operates with a substantially constant frequency under all operating conditions. In another embodiment, the power supply regulator operates with a substantially constant frequency under a fixed range of operating conditions
In yet another aspect of the present invention, a switched mode power supply includes a power supply input and a power supply output. A power supply regulator is coupled to the power supply input and an energy transfer element input. The energy transfer element is further coupled to the power supply output. The power supply regulator has an operating frequency and a threshold to detect the peak energy transfer element input current. In one embodiment, the operating frequency and/or the peak current detection threshold of the power supply regulator are adjusted to maintain the product of the square of the peak current limit and the operating frequency substantially constant from one power supply regulator to another. In one embodiment, the switched mode power supply is a flyback converter. In another embodiment, the switched mode power supply is a buck converter. In one embodiment, the power supply regulator operates with a substantially constant frequency under all operating conditions. In another embodiment, the power supply regulator operates with a substantially constant frequency under a fixed range of operating conditions.
In still another aspect of the present invention, a switched mode power supply includes a power supply input and a power supply output. A power supply regulator is coupled to the power supply input and an energy transfer element input. In one embodiment, the power supply regulator has a fixed operating frequency when the switched mode power supply is providing substantially maximum output power. In one embodiment, the power supply regulator has a threshold to detect the peak energy transfer element current. In one embodiment, the operating frequency and/or the peak current detection threshold of the power supply regulator are adjusted during the manufacture of the power supply regulator to maintain the product of the square of the peak current limit and the operating frequency substantially constant from one power supply regulator to another. In one embodiment, the switched mode power supply is a flyback converter. In another embodiment, the switched mode power supply is a buck converter.
Additional features and benefits of the present invention will become apparent from the detailed description and figures set forth below.